(1) Field of the Invention
The present invention relates to a system to control an industrial robot (hereinafter referred to simply as a "robot").
(2) Description of the Prior Art
A robot normally comprises a robot arm into which a servomotor has been incorporated, and the said servomotor is driven by a servo-amplifier unit. The control of the robot is performed by aiving commands to the servo-amplifier unit by a controlling device. FIG. 5 is a schematic block diagram to explain the conventional robot controt. Incidentally, in FIG. 5 a robot in a form shown in Japanese Patent Application Laid-Open No.8-11074 specification for example is shown as an example of the conventional robot.
A controlling unit 1 controls a servo amplifier unit 2, and, based on the control the servo amplifier unit 2 supplies a power to a servomotor 31 of a robot unit 3. The servomotor 31 is incorporated into every robot arm 32, and controlled by the controlling unit 1 via the servo amplifier unit 2.
Between the controlling unit 1 and the servo amplifier unit 2, the controlling unit 1 sends a PWM command to the servo amplifier unit 2 and obtains a current feedback value from the servo amplifier unit 2. In addition, between the controlling unit 1 and the robot 3, the controlling unit 1 outputs an output for an end effector to the robot 3 and inputs a servomotor speed feedback signal, a servomotor position feedback signal an end effector input signal and a robot overtravel signal from the robot 3.
The controlling unit 1 conducts current control of a servo motor system based on the current feedback value, and speed control or position control of the servomotor system based on the servomotor speed feedback signals or the servomotor position feedback signls. In addition, by input and output signals for the end effector, control of every kind of function which the robot comprises is conducted by a robot overtravel signal whereby an over movement of the robot arm is detected.
In addition, Japanese Patent Application Laid-Open No.8-229862 discloses placing a servo amplifier in the vicinity of a motor mounted on a body of the robot for the purpose of making wiring of power cables shorter.
There is a problem in the conventional robot control systems that for the purpose of conducting transmission and reception of every kind of signal such as controlling signals, feedback signals, detection signals, et wiring between the robot and the servo amplifer unit, the servo amplifier unit and the controlling unit, and the robot and the controlling unit becomes necessary, resulting in an increase in the number of wiring.
In addition, in the case where the control unit is placed at a position far from the robot as well as the servo amplifier unit, it is necessary to extend two cables, namely the cable connecting the controlling unit and the servo amplifier unit and the cable connecting the controlling unit and the robot. In the conventional configurations, each time when a controlling unit is placed at a different position, as such a cable connecting the controlling unit and the servo amplifier unit and the cable connecting the controlling unit and the robot, it is necessary to prepare a plural kinds of cables having lengths corresponding to the position of a controlling unit to be placed.
Therefore, in the conventional robot controlling systems, there are problems in terms of the number of wirings, the number of extension cables, kinds of lengths in stock cables. An increase in the number of wiring as well as the number of kinds and units, etc. of extension cables to be deployed in advance causes an increase in costs and wirng work, resulting in a troublesome control in cables and wiring inside cables. Also there are problems in terms of appearance of covering of wiring.
In addition, in the previously described well known example (Japanese Patent Application Laid-Open No.8-229862), wiring of power cable gets shorter. Nevertheless, as concerns wiring for transmitting servomotor speed and position feedback signals, input and output signals for an end effector, and robot overtravel signals no consideration has been given to shorten wiring